Twenty years ago, I was invited to the scariest party imaginable. It was in New York at the legendary Bemelmans Bar, an exquisite Fabergé egg of a place in The Carlyle hotel. Having plucked up courage to attend, I executed a sort of crablike shuffle to get past the herd of giraffe-like supermodels necking near the entrance and sought refuge in a dimly-lit booth occupied by an older woman. Maybe she would be a friendly person to chat to until Himself showed up?

Too late, when the woman tilted her head into the light from a candle, did I notice a cheekbone you could open a manila envelope with. I recognised that cheekbone. It came attached to a Hollywood legend – Lauren Bacall. Not, shall we say, a notably cosy person. I leapt up and escaped to stand by the piano in the middle of the room. Surely, nothing could go wrong there?

By chance, the pianist started playing the opening song from one of my favourite musicals, Stephen Sondheim’s Company. In that intimidating place, it felt like coming upon an old friend. I started humming along, mouthing the words I knew by heart. I don’t know how long it was before I noticed a man with a neat grey beard who had suddenly appeared by my side the piano. “This is my favourite musical,” I told him, hoping to break the ice (boy, was it icy).

How long was it before I recognised the man – OH, PLEASE, GOD, NO! – and started babbling excuses? “I had no idea. I mean, obviously, I know who you are, but I didn’t just say it was my favourite musical because, er, you wrote it.” I wish I could say that Sondheim laughed off my gaucheness. But he was a testy fellow, as geniuses can be, so I fled.

He died a week ago at the age of 91 and, despite that great age, there was a vast that the world had lost someone irreplaceable. Famously, Sondheim wrote “musicals for people who don’t like musicals”. And people who love musicals sometimes found Sondheim too cool, too clever clever. He was sniffy about West Side Story, his early, monumental success, correctly pointing out that a Puerto Rican girl who worked in a bridal shop would never have sung (in “I Feel Pretty”): “It’s alarming how charming I feel.”

He did have a weakness (I call it strength) for those fiendishly clever rhymes. In “Getting Married Today”, a hyperventilating bride, cries: “Perhaps / I’ll collapse / In the apse.”

The actor Mandy Patinkin, who worked with the maestro many times, said: “I got to be in the room with Shakespeare.” Personally, I would place Stephen Sondheim alongside Andrew Marvell and John Donne; he would have made a fabulous metaphysical poet.

By happy coincidence, Steven Spielberg’s film of West Side Story is about to be released and a new audience will get to appreciate those extraordinary lyrics. Has any writer better fixed for ever the thrilling sense of impending love as Sondheim did in Something’s Coming (“Could be! Who knows?”)? Or written a lovelier song about a woman’s name (“All the beautiful words of the world in a single word: Maria, Maria, Maria, Maria”)?

Sondheim could make you laugh out loud while sticking a knife in your heart. As in The Little Things You Do Together where a wife delivers a caustic, pitch-perfect analysis of her long marriage:

“It’s the little things you share together,
Swear together
Wear together
That make perfect relationships
The concerts you enjoy together
Neighbours you annoy together
Children you destroy together
That keep marriage intact.”

That song is from Company, one of my favourite works of art. I tried to tell its composer that – very badly – all those years ago in Bemelmans Bar. Ah, well. Stephen Sondheim is with the immortals now.